I am happy to announce that we open-sourced EmulatedBitIntegers.jl. The package allows defining arbitrary bit width integers like UInt3 or Int7 which behave mathematically as you would expect, by overflowing and underflowing like a native implementation would do.
Internally, the package stores the values in a storage type which is a regular (non-emulated) primitive bit integer like UInt8. By implementing the Julia Base methods, the user normally does not need to know this except for two things
- Storage space might be larger than expected, e.g. if you have a struct with two
UInt4values it will be 2 bytes instead of a single byte. But see the announcement for PackedStructs.jl how to avoid this. - Using them can be a bit slower due to the overflow and underflow guarantee which needs additional instructions in general.
That being said the package is highly performance optimized and for all I know generates the same machine code as a future Julia-native LLVM-based approach will generate (at least with Julia 1.12 and 1.13; Julia 1.10 lacks some LLVM optimizations). With all the progresses in superscalar processor architectures we have seen in the last two decades, there is no performance difference between the emulated bit integers and the native bit integers more often than not.
Related Work
-
Simen Gaure added a pull request to
BitIntegers.jlwhich implements support for arbitrary bit integers viallvmcall. -
Work is ongoing to support arbitrary bit integers directly in Julia, see e.g. Julia #45486 and Julia #61359. I would be glad if this work makes EmulatedBitIntegers.jl obsolete.
Thanks to the nice people in JuliaData, who kindly allowed me to move and maintain the code there.